Ultrastructure at the Host-Parasite Interface of Phytophthora capsici in Roots and Stems of Capsicum annuum

The infecting hyphae of Phytophthora capsici grew intercellularly in infected tissues of roots and stems of pepper (Capsicum annuum). The vascular tissues were not markedly disorganized even when heavily infected. Intercellularly growing hyphae penetrated the host cells by forming haustorium-like bodies. The consistent features of ultrastructural changes in infected tissues of pepper roots and stems were degeneration of cell organelles and dissolution of host cell walls. The cytoplasm detached from the cell wall aggregated abundantly around some haustorium-like bodies or the penetration sites of fungal hyphae. The host cell walls were palely stained, thinned and swollen, possibly being biochemically altered by the action of fungal macerating enzymes. Electron-dense, wall-like material was apposed on the outer wall of xylem vessel contacted by fungal hyphae. The infecting hyphae were also surrounded by granular, dark-staining cytoplasm. Characteristics of host cell responses to the invading P. capsici were the deposition of papilla-like material on host cell walls next to hyphae and the encasement of haustorium-like bodies with wall appositions.     

Soluble Proteins, Esterases and Superoxide Dismutase in Stem Tissue of Pepper Plants in Relation to Age-related Resistance to Phytophthora capsici

Patterns of soluble proteins and isoenzymes of esterase and superoxide dismutase were investigated in healthy and infected stems of two pepper cultivars resistant and susceptible to Phytophthora capsici. By the use of two-dimensional SDS-polyacrylamide gel electrophoresis, it was possible to compare precisely the cultivars Hanbyul and Kingkun susceptible or resistant to P. capsici with respect to their protein patterns. The two-dimensional electrophoresis identified three proteins (25—27 kD) from the healthy stem extracts of Kingkun, which were absent in Hanbyul. Some particular proteins appeared in pepper stems of both cultivars at later developmental stage of plants, suggesting their role in the expression of age-related resistance. Some proteins which were not detectable in the healthy stem extracts also existed in large amounts in the diseased ones. By contrast, other proteins present in the healthy stems disappeared from the diseased stems. Some esterase isoenzymes appeared in the two cultivars only at late developmental stage. Other esterase isoenzymes were produced only in the diseased stems. There were no differences in the patterns of superoxide dismutases between the cultivars and also between developmental stages. Large activities of several superoxide dismutases were detected in the diseased stems.